Keyswitches for electrical keyboards may be either of the mechanical contact type or of the analog contactless type, wherein a magnet controls the actuation state of the switch by determining the saturation state of a closed-loop magnetic core that is threaded by drive and sense lines.
The mechanical type of keyswitch has the advantage of being relatively low in cost, and for many applications this factor makes it desirable to employ such a mechanical keyswitch. However, mechanical keyswitches have a number of disadvantages that make them undesirable for use in applications where high reliability is required and the added cost of a analog switch is, therefore, considered to be warranted. These disadvantages include contact bounce, the possibility of arcing, lower life times due to pitting and corrosion and possible deformation of the contact members.
Analog switches, such as the magnetic saturable core, offer greatly improved reliability, but at a higher cost. In addition, such switches generally require some sort of circuit modification to supply "hysteresis," or a reduced sensitivity of the sensing circuit after a keyswitch has been actuated to prevent electrical noise from producing false output signals. In applications where high reliability is necessary, however, analog switches provide the utmost in dependability and endurance.
It would be desirable for keyboard manufacturers to have the capability of making keyboards with either type of keyswitch, in accordance with their customer's wishes. However, previously this has required the manufacture and stocking of two separate types of keyswitches, with added cost and complications.
The electrical keyswitch of the present invention provides a simple electrical keyswitch that is capable of being operated either as an analog magnetic type of contactless keyswitch or as a mechanical type of keyswitch with only minor modifications being necessary to convert from one to the other, due to the improved design provisions that are provided for the keyswitch. In addition, for special applications, both types of keyswitches could be simultaneously incorporated into one keyswitch component if desired.
The keyswitch of the present invention is designed to accept flat drive and sense line conductors, wherein these conductors could be inserted into the switch with automatic machinery. The magnetic sensing core is positioned onto one leg of a U-shaped drive line and onto one leg of a U-shaped sense line and the core with the two linking lines is then inserted into a retaining well formed on the base of the keyswitch from the top of the switch. The retaining well is formed by a walled configuration that consists of a pair of vertically extending walls that project upwardly from the horizontal surface on the base of the keyswitch. Each of the retaining walls has a groove in it and the horizontal surface has a slot through it which runs beneath the grooves and the walls so that the drive and sense line conductors may be positioned through the horizontal surface in the upstanding walls as the magnetic core is positioned in the retaining well. The magnetic core and the drive and sense lines are retained in the base of the keyswitch only by closeness of the fit between the drive lines and the receiving portions of the base. Thus, a defective magnetic core may be easily removed merely by pressing upwardly on the leads so that the leads and the core are removed from the keyswitch without disassembly of any portion of the device. This improved design allows for rapid replacement of defective sensing cores while at the same time, by confining the analog switching components to the exterior of the plunger and to one side of the base of the keyswitch, allows the interior of the keyswitch to be used to retain the mechanical switching components therein.